Coloration of sheet materials



Patented Aug. 12, 1952 .lolin Allan,

Finningley Oxley,

signers to Celanese No Drawing.

Application April Spondon, near Derby, 'andHorace.

Charmouth, England, as- Corporation. of- America, a, .corporatiohcfDelaware 29, 1949,"Ser ial= No. $0,534. In .Great Britain May 10, 1948:

This invention relates to the colouraticn of transparent or translucentsheets of thermoplastic. derivatives or like polymers. 7

The various methods hitherto available for locally colouring sheetmaterials of the kind referred to above, and especially the methodsavailable for printing rigid sheets have been defective with respect tothe bloom, transparency and fast ness to. rubbing of the colourationsobtained.

We have found that local colourations of very good bloom, transparencyandfastness to'rubbing can be obtained on such materials by transferringto selected areas of the sheet, a dyesoluble in the sheet-materialunaccompanied by any substance insoluble in said material, andsimultaneously or subsequently subjecting the sheet to pressure'appliedby means of a polished surface at a temperature above the flow-point cfthe sheet-material. By the flow-point of the sheet material is meant thetemperature at which that material will flow 1" in a V3" diameter tubein 2 minutes under a pressure of 1000 lbs. per square inch. 7 Theinvention will be described with particular reference to colouringsheets of plasticised cellulose acetate. One method of carrying out theinvention is to press on to the sheet material a cellulose acetatefabric printed with colours soluble in cellulose acetate, the pressureand temperature being sufficient to cause the plasticised celluloseacetate to flow without melting the cellulose acetate fabric. Thus, forexample, a cellulose acetate fabric printed with the desired pattern'inwaterinsoluble dyes having affinity for cellulose acetate, steamed,washed and dried, may be laid upon the, sheet of cellulose acetate to beprinted and the assembly placed between highly polishedsteel platens ina steam-heated press and pressed at 150 to 180 C. under 150 to 30% lb.per squareinch pressure for a few minutes. After removing the assemblyfrom the press and allowing it to cool, the fabric can readily beseparated from the sheet material which will be found to have taken thedesign of the printed fabric in bright transparent colour, and to showalso an attractive em bossed fabric-effect.

The preliminary printing of. the cellulose acetate fabric may be carriedout in the ordinary way using a printing paste thickened, for eX- ample,with methyl cellulose or other suitable thickener. If attempts are madeto print directly on to cellulose acetate sheet using pastes containingsuch thickeners, i.- e. thickeners which are incompatible with thesheet-material,-.the

presence of the V marsthe eifect-obtained, giving an undesirabledullness to thecolourations. When howeventhe design is transferred froma printed fabric as 7 described, this dulling of thecolours doesnotoccur.

If, instead of using a fabric of cellulose acetate aprintedcottongfabric is used, difficulty;

is experienced in-separating the fabric froinjhe printed; sheet'material, This difficulty, "be somewhat; reduced byusing;;a,fab1jic; figh twisted Egyptian yarns Well singed. "The same difficulty isexperiencedgwhen; th printed fabric isreplacedby a printed paper. Inthis case it is of. some advantage to use a. heavily, pigmentedpaper'heavily calendered, but neither wit-hen Egyptian cotton fabric ofthe kind specified nor with a pigmented paper print have the results:been nearly as satisfactory as Whenaprintedcellulose acetate fabric isused. Linear polymers in which the dyes used are soluble, .e. g. nylon,:can be used successfully. Other linear polymers have ing the desiredsolubility properties include: other lower fatty-acid esters of;cellulose i. e. esters derived from; fattye-acids containing. 2..toL4c'ar.bon atoms, e. g. cellulose propionate, cellulose butyrate,cellulose acetate-propionate or cellulose ac-etate-butyrate, as wellias.cellulosezetherszsuch. as ethyl cellulose andbenzyl .cellulose. v

A second method-of carrying-out theinvention' is to print the requireddesign on a polishedmetal plate, e. g"- by screen printing, in the:form-:.of a. cellulose acetate lacquer, or other lacquer-,zwhich iscompatible-withthe materialof which the sheet is composed (bywhichismeantthat all the con-- stituents. ofthe lacqueriare solublelinthe sheet material) andafterdrying,to'fassemble the plate in contactwith the sheet to, becoloure'djin a heated platen press .and subject the,ass embly...to heat and pressure as described. above. on removing the,assembly fromthepress, cooling, and sepa: ratingthe metal plate from thecelluloseacetate sheet, the sheet is found to exhibit the-desired.colour-effects. v

A further roethodbfcarrying. .out the inyention is to print directly onto the cellulose acetate sheet by the silk-screenprocess using acellulose acetate lacquer compatible with cellulose acetate andcontaining a dy whichis solubleiincellulose acetate, and after the printhas driedgtopress the printed sheet betweenpolished metal'platens atsuch temperatures and pressures as arereferred to above. In. this.wayalso colcurseffects, are obtained whichare-bright,transparent,t.andi

remain fast to rubbing. fllhis;meth'cidtcan bezap-t thickener on the;printed sheet.

3 plied to unpolished sheets as obtained from a block-slicing operationto give printed sheets of very satisfactory finish.

An essential feature of the invention is the use as the colouring agentof a dye which is soluble in the sheet-material to be coloured. Forcellulose esters and ethers those azo-dyes, nitrodiarylamine dyes, andamino-anthraquinone dyes, which are water-insoluble and have affinityfor the cellulose derivative, are generally suitable, and many of thesedyes are also suitable in the colouration of sheets having a basis of acondensation polymer such as nylon or an addition polymer such aspolymethyl methacrylate.

Although the transfer with the colour of any substance incompatible withthe cellulose derivative or other polymer is to be avoided ifcolourations of high transparency are required, the invention includes aprocess in which a pigment, especially a white pigment is transferred tothe sheet material in areas along-side the areas coloured by the dye.The most attractive effects have been obtained using pigments of highrefractive index, e. g. titanium dioxide of refractive index greaterthan 2. The pigment may, for example, be contained in a lacquer used toprint directly onto the cellulose acetate sheet or may be used inpreparing a printing plate for printing a coloured design upon the sheetmaterial.

The following examples, in which all the parts are by weight, illustratethe invention:

Example 1 A" plain woven cellulose acetate fabric was printed with apaste of the following composition:

200 parts 4-nitro2'-chlor-4-dioxy ethylaminoazo-benzene 80 parts water120 parts ethyl alcohol 24 parts methyl cellulose The printed fabric wasthen steamed to fix the colour, washed and dried.

On the lower platen of a steam heated press were assembled in thefollowing order:

3 sheets of cellulose pulp;

A polished stainless steel platen;

The printed fabric with the printed face uppers most;

A sheet of plasticised cellulose acetate 4 mm.

thick.

The press was then closed and the assembly subjected to a pressure of200 lb. per square inch for two minutes at 180 C. The press was thenopened, the assembly allowed to cool and the fabric separated from thesheet.

In this way a coloured pattern of fine bloom and transparency wasobtained on the cellulose acetate sheet. The sheet showed also anattractiveembossed effect derived from the structure of the fabric.

The cellulose acetate fabric can be replaced by a fabric ofpoly-hexamethylene adipamide.

Example 2 200 parts of a 50 aqueous titanium dioxide paste 80 parts of a60% aqueous albumin paste 8 parts ammonium hydroxide 30 parts glycerol82 parts water 24 parts methyl cellulose During the pressing operationthe titanium dioxide was transferred to the cellulose acetate sheetforming areas of dull lustre alongside the areas of bright transparentcolour.

Example 3 A pattern was formed by screen printing on to a metal printingplate the following composition:

60 parts 4-nitro-2'-chlor-4dioxy ethylaminoazo-benzene 60 partscellulose acetate 16 parts dimethyl phthalate 4 parts triphenylphosphate 270 parts acetone 280 parts ethyl lactate 20 parts glycoldiacetate Example 4 A rigid unpolished sheet of plasticised celluloseacetate, sliced from a block, was screen printed with the composition ofExample 3. The printed sheet was allowed to dry and was then insertedbetween two polished stainless steel platens in a steam-heated press.The sheet was pressed at about C. under a pressure of 200 lbs. persquare inch for two minutes.

In this way the sheet was given a high polish on both surfaces and acoloured pattern of high transparency and bloom on one surface.

Example 5 The process was carried out as in Example 4, save that thelower platen, instead of being pol ished, was engraved with a finepattern so as to roughen the whole lower surface of the celluloseacetate sheet. The effect was to increase the brightness of thecolourations when viewed by reflected light.

Example 6 The process was carried out as in Example 3, except that,after printing the plate with the coloured composition, it was alsoscreen-printed with the following composition:

60 parts milled titanium dioxide 60 parts cellulose acetate 16 partsdimethyl phthalate 4 parts triphenyl phosphate 280 parts ethyl lactate240 parts acetone 20 parts glycol diacetate Using this printing plate,colourations similar to those referred to in Example 3 were obtainedwith areas of low lustre alongside the coloured areas.

Example 7 The process was carried out as in Example 5, except that afterprinting with the coloured composition, areas alongside the colouredareas were printed with the titanium dioxide composition of Example 6. Ahighly polished sheet with a pattern comprising brightly coloured areasand areas of dull lustre was obtained.

In these examples the cellulose acetate sheet material can be replacedby sheet material having a basis of cellulose acetate-butyrate,cellulose acetate-propionate, cellulose propionate or polymethylmethacrylate, and the dye specified can be replaced by2:4-dinitro-4'-amino-diphenylamine, 1 :4 dimethylamino anthraquinone oralpha-1-ethylaminoanthraquinone. Any of the cellulose esters specifiedcan be used as the basis of the lacquers used in Examples 3 to 7 insteadof cellulose acetate.

The brightness of the colourations obtained when viewed by reflectedlight may be increased by roughening the uncoloured surface of thesheet. This may be done, for instance, as illustrated in Example 5, bypressing that surface against a hot surface having the necessary roughtexture.

The process of the invention may be employed in the colouration ofthick, substantially rigid transparent or translucent thermoplasticsheet material as well as of thin, flexible films (including foils)Having described our invention, what we desire to secure by LettersPatent is:

1. Process for locally colouring self-supporting sheets of a plasticizedcellulose fatty-acid ester in which the acid radical contains 2 to 4carbon atoms, which comprises printing onto a textile fabric ofcellulose acetate a counterpart of the coloured pattern required,putting together the coloured surface of the fabric and that surface ofthe sheet which is to be coloured, applying pressure to the back surfaceof the fabric by means of .a polished surface at a temperature above theflow-point of the sheet-material to.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,883,854 Michael Oct. 18, 19321,981,472 Schneider Nov. 20, 1934 2,353,717 Francis et a1. July 18, 19442,404,073 Karfiol et a1. July 16, 1946 2,510,750 Marquardt June 6, 19'50FOREIGN PATENTS Number Country Date 562,573 Great Britain July 6, 1944

1. PROCESS FOR LOCALLY SELF-SUPPORTING SHEETS OF A PLASTICIZED CELLULOSEFATTY-ACID ESTER IN WHICH THE ACID RADICAL CONTAINS 2 TO 4 CARBON ATOMS,WHICH COMPRISES PRINTING ONTO A TEXTILE FABRIC OF CELLULOSE ACETATE ACOUNTERPART OF THE COLOURED PATTERN REQUIRED, PUTTING TOGETHER THECOULOURED SURFACE OF THE FABRIC AND THAT SURFACE OF THE SHEET WHICH ISTO BE COLOURED, APPLYING PRESSURE TO THE BACK SURFACE OF THE FABRIC BYMEANS OF A POLISHED SURFACE AT A TEMPERATURE ABOVE THE FLOW-POINT OF THESHEET-MATERIAL TO CAUSE TRANSFER OF THE DYE FROM THE FABRIC TO THESHEET, AND SEPARATING THE FABRIC AND SHEET.